Conventionally, in pneumatic tires (hereinafter, referred to as tires) mounted on passenger cars, for example, a method for forming a plurality of circumferential grooves in a tread has been widely used in order to ensure a water drainage performance on a wet road surface.
For example, there is known a tire provided at groove bottom portions of circumferential grooves thereof with projections inclined with respect to center lines of the circumferential grooves in a tread in order to facilitate the drainage of rainwater that has entered the circumferential grooves (for example, Patent Document 1). With such a tire, a water flow is generated in the rainwater that has entered the circumferential grooves, resulting in the improvement of a water drainage performance.
However, the above-mentioned conventional tire has the following problems. That is, the tire having groove bottom portions provided with projections has a problem that a buckling, that is, the tread is warped inward in the tire radial direction in the vicinity of the circumferential grooves, starting from the projections, easily occurs. If the buckling occurs, a ground contact shape of the tread is not stable, and as a result, braking performance is reduced.
Meanwhile, in order to suppress the occurrence of the buckling in the vicinity of the circumferential grooves, reinforcing the groove bottom portions of the circumferential grooves or wall surfaces of land portions forming the circumferential grooves is also considered. This case leads to another problem that the sectional area (volume) of the circumferential groove is reduced, resulting in the deterioration of a water drainage performance.